1. Field of the Invention
This invention relates to the coating of filamentary articles. In particular continuous filaments are uniformly and concentrically coated.
2. Description of the Prior Art
In the field of optical glass fibers, it is desirable to coat a continuous glass fiber filament with a coating material in order to protect and strengthen the filament. In the prior art such continuous glass fiber filaments are coated by the extrusion of plastic as set forth in U.S. Pat. No. 3,960,530, which issued to R. Iyengar on June 1, 1976. That patent discloses a closed vertical cylinder charged with plastic coating material. The cylinder has a die aperture in the lower end thereof and an axial core tube terminating in the die aperture to form an annular orifice, the plastic being liquified to pass through the die orifice. The glass fiber filament is drawn from a source of molten glass coaxial with the core tube, continuously through the core tube. Pressurized gas is introduced into the upper portion of the cylinder to force the liquified plastic through the annular orifice and onto the filament as it leaves the axial core tube.
Such extrusion application of the plastic coating induces undesirable stresses in the coating material as it passes through the die orifice and, in addition, the drawing speed of the glass fiber filament is limited due to the relatively slow application speed of the extrusion process.